1. Field of the Invention
The present invention relates to a pellicle for lithography that is used as a debris shield for a lithographic mask when producing a liquid crystal display panel or a semiconductor device such as an LSI or a ULSI.
2. Description of the Related Art
In the production of a semiconductor such as an LSI or a ULSI or the production of a liquid crystal display panel, patterning is carried out by irradiating a semiconductor wafer or a liquid crystal master plate with light; if debris is attached to an exposure master plate used here, since the debris absorbs the light or bends the light, there are the problems that the replicated pattern is deformed, the edge becomes rough, or the background is stained black, thus impairing the dimensions, quality, appearance, etc. The ‘exposure master plate’ referred to in the present invention is a general term for lithographic masks and reticles.
These operations are usually carried out in a clean room, but even within a clean room it is difficult to always keep the exposure master plate clean, and a method is therefore employed in which a pellicle that allows exposure light to easily pass through is adhered to the surface of the exposure master plate to act as a debris shield.
In this case, the debris does not become attached directly to the surface of the exposure master plate but becomes attached to the pellicle film, and by focusing on a pattern of the exposure master plate when carrying out lithography the debris on the pellicle film does not become involved in the replication.
A pellicle is basically constituted from a pellicle frame and a pellicle film stretched over the frame. The pellicle film is formed from nitrocellulose, cellulose acetate, a fluorine-based polymer, etc., which allows exposure light (g rays, i rays, 248 nm, 193 nm, 157 nm, etc.) to easily pass through. The pellicle frame is formed from a black-anodized etc. A7075, A6061, A5052, etc. aluminum alloy, stainless steel, polyethylene, etc. The pellicle film is adhered by coating the upper part of the pellicle frame with a good solvent for the pellicle film and air-drying (ref. JP-A-58-219023 (JP-A denotes a Japanese unexamined patent application publication)) or by means of an adhesive such as an acrylic resin, an epoxy resin, or a fluorine resin (ref. U.S. Pat. No. 4,861,402, JP-B-63-27707 (JP-B denotes a Japanese examined patent application publication), and Japanese registered patent No. 3089153). Furthermore, since an exposure master plate is mounted on a lower part of the pellicle frame, a pressure-sensitive adhesion layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin, etc. and a reticle pressure-sensitive adhesive protecting liner for the purpose of protecting the pressure-sensitive adhesion layer are provided.
The pellicle is installed so as to surround a pattern region formed on the surface of the exposure master plate. Since the pellicle is provided in order to prevent debris from becoming attached to the exposure master plate, this pattern region and a pellicle outer part are separated so that dust from the pellicle outer part does not become attached to the pattern face.
The present applicant has disclosed a filter-equipped pellicle in which a filter that is to be provided on an atmospheric pressure adjustment hole is wetted with a pressure-sensitive adhesive (ref. JP-A-9-68792).
In particular, since the pellicle is used by affixing it directly to an exposure master plate, there is a desire for a low gas generation rate for materials forming the pellicle, that is, a reticle adhesive, a film adhesive, an inner wall coating agent, etc., which are formed from organic materials, and improvements have been made. Among them, as the reticle adhesive there is one that employs a silicone resin in order to give lower outgassing, improved UV resistance, and improved chemical resistance. Since silicone resins have excellent chemical stability, it is possible to fix a pellicle onto a reticle without there being any changes over a long period of time. However, when the pellicle is to be stripped from the reticle for replacement, it is difficult to carry out stripping well without leaving a residue on the reticle. As a method for stripping a pellicle that has a silicone adhesive, a method in which a substrate from which a pellicle is stripped is heated has been proposed (Patent Publication 1).
In recent years, the LSI design rule has shrunk to sub-quarter micron, and accompanying this the control of foreign matter has become tighter. There is also a demand for flushing with clean air a closed space formed by affixing a pellicle and then carrying out exposure, and the role of the atmospheric pressure adjustment hole of the pellicle frame has become all the more important.
As described in JP-A-9-68792 above, measures against foreign matter with respect to a filter provided on an atmospheric pressure adjustment hole have been proposed, but no measures taken have given a marked improvement for the pellicle frame atmospheric pressure adjustment hole itself.